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The distribution of warm gas in the G327.3--0.6 massive star-forming region

Most studies of high-mass star formation focus on massive luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at characterising the effects of clustered star formation and feedback of massive stars on the surrounding medium by studying the distribution of warm gas through mid-J 12CO and 13CO data. We present APEX 12CO(6-5), (7-6), 13CO(6-5), (8-7) and HIFI 13CO(10-9) maps of the star forming region G327.36-0.6. We infer the physical properties of the emitting gas on large scales through a LTE analysis, while we apply a more sophisticated LVG approach on selected positions. Maps of all lines are dominated in intensity by the PDR around the Hii region G327.3-0.5. Mid-J 12CO emission is detected over the whole extent of the maps with excitation temperatures ranging from 20K up to 80K in the gas around the Hii region, and H2 column densities from few 10^21 cm-2 in the inter-clump gas to 3 10^22 cm-2 towards the hot core G327.3-0.6. The warm gas (traced by 12 and 13CO(6-5) emission) is only a small percentage (10%) of the total gas in the IRDC, while it reaches values up to 35% of the total gas in the ring surrounding the Hii region. The 12CO ladders are qualitatively compatible with PDR models for high density gas, but the much weaker than predicted 13CO emission suggests that it comes from a large number of clumps along the line of sight. All lines are detected in the inter-clump gas when averaged over a large region with an equivalent radius of 50" (~0.8pc), implying that the mid-J 12CO and 13CO inter-clump emission is due to high density components with low filling factor. Finally, the detection of the 13CO(10-9) line allows to disentangle the effects of gas temperature and gas density on the CO emission, which are degenerate in the APEX observations alone.